1. The Field of Invention
The invention is in the field of alarm systems, electronic fence and more general, in the field of security and defense systems.
2. The Prior Art
An illegal tunneling activity is conducted by terrorists, smugglers, or prisoners under an above-ground fence protecting a facility, a border, or a prison, respectively. The search for counter measures is a continuous effort by border control police departments, prison managements and defense departments all over the world. Butler (Geophysics, 49, 108496, 1984) suggested to use microgravity measurements to located tunnels. However, the needed equipment is expensive and cumbersome and the method is not sensitive enough.
Similarly, a press release by Western Kentucky University at May 18, 2006, reports on a robot which is “an all-terrain vehicle operated via a laptop computer carries a microgravity meter to locate underground voids, sinkholes, caves or, in the case of the US-Mexico border, clandestine tunnels”. (http://www.wku.edu/news/release06/may/printer/robot.html)
Robots were proposed in the prior art for deep drilling. Liu et al (Y. Liu, B. Weinberg, C. Mavroidis, “Mechanical design and modeling of a robot planetary drilling system”, Proc. of IDETC/CIE 2005) describe a robot for deep drilling in Mars. U.S. Pat. No. 7,055,625 to Myrick and Gorevan, issued Jun. 6, 2006, describes an autonomous subsurface drilling device with an ability to drill both forward and rearward.
Two U.S. patents address finding an intrusion point in a fence. U.S. Pat. No. 7,126,475 to So, issued Oct. 24, 2006 deals with a fence wire buried in a yard. U.S. Pat. No. 7,184,907 to Chun, issued Feb. 27, 2007 describe a monitoring system of a fiber optic cable, attached to a security fence, which determines the length of the fiber optic cable between a monitoring system and an intrusion point.
U.S. Pat. No. 6,778,469 to MacDonald, issued Aug. 17, 2004, describes a harbor fence “comprises a series of spars that protrude above the water surface, that are spaced approximately uniformly and that are connected to an electrical computer with a telemetry subsystem. Each spar contains electronic sensor, e.g. water immersion sensors and accelerometers and circuitry to detect intrusion an to communicate the location of the intrusion to a computer control station . . . . The embodiment also facilitates deploying and retrieving the harbor fence system”.
The prior art drilling robots are very expensive and quite large, while for preventing underground intrusion along long borders a large number of cheap robots is needed. Going underground is absolutely different from going subsurface in a water environment. Thus, it is an object of the present invention to overcome some of the drawbacks of the prior art, and to address underground intrusion detection in a novel and economic way.